1. Field of the Invention
The present invention relates to a pharmaceutical composition for promoting fertilization comprising cyclic ADP-ribose or its derivative. More specifically, the present invention relates to a pharmaceutical composition for promoting fertilization and a method for promoting fertilization, which can increase sperm motility using cyclic ADP-ribose and CD38, thereby promoting fertilization.
Also, the present invention relates to a pharmaceutical composition for contraception comprising an antagonist of cyclic ADP-ribose. More specifically, the present invention relates to a pharmaceutical composition for contraception and a method for inhibiting fertilization, which can inhibit a pattern of a continuous increase in calcium caused by progesterone to inhibit sperm motility, thereby inhibiting fertilization.
2. Description of the Prior Art
Spermatozoa are produced in the testis and undergo post-gonadal modifications in the epididymis to acquire fertilizing ability. In epididymal plasma, high-molecular-weight proteins and such small molecules as free carnitine convert the gametes into competent and functional cells. Free L-carnitine is taken up from blood plasma and concentrated in the epididymal lumen. This epididymal secretion is beneficial for spermatozoa and is not merely an excretory waste. Free carnitine goes through the sperm plasma membrane by passive diffusion. Free L-carnitine is acetylated in mature spermatozoa only. The excess acetyl-CoA from the mitochondria is probably stored as acetyl-L-carnitine and modulates the reserves of free CoA essential to the function of the tricarboxylic acid cycle. This property of L-carnitine of buffering CoA in the mitochondrial matrix is known in somatic cells but is accentuated in male germinal cells. The relationship between the endogenous pool of free and acetylated L-carnitine and the percentage of progressive sperm motility indicates a more important metabolic function. Thus, the potential of initiating sperm motility which takes place in the epididymis is probably independent of the carnitine system while the energy properties of acetyl-L-carnitine is relevant in situations of “energy crisis”. The uptake of cytoplasmic free L-carnitine in mature spermatozoa must be a protective form of mitochondrial metabolism useful to the survival of this isolated cell.
Idiopathic asthenozoospermia, a disorder of sperm motility, is illustrative of certain conditions in this area. It is a post-testicular cause of infertility due to various ethiology, i.e. congenital defects of the sperm tail, maturation defects, immunological disorders or infection. Several drugs for treating idiopathic asthenozoospermia, none of them completely satisfactory, are known.
Antiestrogen drugs (such as clomiphene citrate and tamoxifen) block sex hormones from inhibiting the Follicle Stimulating Hormone (FSH) and the Luteinizing Hormone (LH) in the brain. This triggers an increased release of LH and FSH, which in turn stimulates testosterone production. Increased testosterone level improves spermatogenesis, thus improving sperm density and motility. However, a recent randomized, double-blind, multicenter study of 190 couples by the World Health Organization (WHO) showed no effect of clomiphene citrate. Tamoxifen was claimed to improve sperm concentration but no change in motility was usually detected. As for clomiphene, recent studies did not confirm its efficacy. Testolactone, an aromatase inhibitor, prevents the conversion of testosterone to estradiol. It has been tested in patients with idiopathic oligospermia but contrasting results have raised many doubts on its efficacy. Mesterolone is a synthetic androgen widely used to treat idiopathic male infertility. A recent study sponsored by WHO failed to show any efficacy of this drug. Thus, studies on a method of promoting fertilizing ability by increasing sperm motility are urgently required.
Calcium signaling in sperm is known to be released from the calcium store present in the midpiece and plays an important role in sperm motility, and calcium signaling by progesterone was reported to occur through a new mechanism having no concern with IP3 that is a general calcium signal initiation site (Fabiani et al., Hum. Reprod, 9, 1485 (1994)). Furthermore, it is known that calcium signaling occurring in many cells stimulates RyR, which opens the calcium store by cyclic ADP-ribose, to release calcium into the cytoplasm, but specific mechanisms in sperm and sperm motility have not yet been reported (Arienti et al., Biol. Cell. 91, 51-54 (1999); Harper et al., J. Biol. Chem. 279, 46315-46325 (2004); Mészáros, Nature 364, 76-79 (1993)). However, it is known that sperm has no endoplasmic reticulum, unlike other cells, and SERCA that is an important calcium channel in the intracellular calcium store is not present in sperm, and secretory pathway Ca2+-ATPase is present in place of SERCA (Clapham, Cell 131, 1047-1058 (2007)).
CD38, a cell membrane protein, uses intracellular NAD as a substrate to synthesize cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucletide phosphate (NAADP), which release calcium from intracellular calcium store into the cytoplasm, thereby controlling the various functions of cells (Berridge et al., Nat. Rev. Mol. Cell Biol. 4, 517-529 (2003); Lee H C, Mol. Med. 12, 317-323 (2006)). Also, it was reported that CD38 binds specifically to CD31 present on the surface of other cells so as to perform intracellular signaling (Deaglio et al., Immunol. 1997; 160:395-402).
The mammalian sperm contains granules having a size of several ten to several hundred nanometers, which are prostasomes secreted from the prostate. The prostasomes bind specifically to spermatozoa under weakly acidic conditions similar to the internal conditions of the female vagina, resulting in structural or functional changes (Ronquist and Brody, Biochim. Biophys. Acta 822, 203-218 (1985); Arienti et al., Membr. Biol. 155, 89-94 (1997); Publicover et al., Nat. Cell Biol. 9, 235-242 (2007); Burden et al., Hum. Reprod. Update 12, 283-292 (2006)). The binding of prostasomes to spermatozoa is known to increase sperm motility (Fabiani et al., Hum. Reprod. 9, 1485-1489 (1994); Arienti et al., Biol. Cell 91, 51-54 (1999)), and it was reported that the intracellular calcium content of spermatozoa bound to prostasomes was increased (Arienti et al., Biol. Cell 91, 51-54 (1999)), but a mechanism which is involved in calcium release by prostasomes has not yet been known. The results of analysis of prostasomes by proteomics techniques indicated the presence of several hundred proteins, including CD38 that is the typical enzyme of ADP-ribosyl cyclase (Palmerini et al., Cell Calcium 25, 291-296 (1999)), but the functional role of the proteins or the correlation of the proteins with other molecules has not yet been elucidated.
It has been reported that prostasomes present in sperm contain various proteins, including CD38 (Palmerini et al., Cell Calcium 25, 291-296 (1999)), and it was reported that a protein group important in the signaling pathway of cyclic SDP-ribose synthesized by CD38 is transferred into spermatozoa (Park et al., Science Signaling, 4, 31-41 (2011)), in which the protein group typically includes progesterone receptor, vacuolar-type H+-ATPase, ryanodine receptor, secretory pathway Ca2+-ATPase, and novel ADP-ribosyl cyclase different from CD38.
Thus, it is needed to find the relationship between prostasomes and sperm motility and find a substance that regulates sperm motility. Also, a new study on a method capable of regulating fertilizing ability by regulating sperm motility based on these findings is required.